The effect of thermal recycling on the metastable structure of potassium ferrocyanide single crystals

The electrical conductivity (sigma) and the dielectric permittivity (epsilon) of pure potassium ferrocyanide (KFCT) single crystals are measured in the temperature range 77-300 K. The effect of cooling and heating recycling on the behaviour of both sigma and epsilon is discussed. The Curie-Weiss law is found to be obeyed in a wide temperature range of the paraelectric phase with constants C0- = 352 K and T0 = 247.2 K. The ratio between the slopes of the two lines representing 1/epsilon versus T in both the ferro- and the paraelectric phases verify the thermodynamic relations. The structural transformation from the tetragonal metastable state to the monoclinic stable state may not be completed through the first cooling process down to about 218 K and the steady state, perhaps, needs further thermal recycling.